The present invention relates to a process for kiln drying wood. In known drying processes hot air is blown over sawn unseasoned timber in stacks, each piece separated from its neighbour by a small spacer strip, and the humid air leaving the stacks of timber is dehumidified, reheated and recycled over the timber. The time taken for drying is determined by the maximum temperature to which the wood can be subjected since cracking, warping and splitting occur if the air blown over the wood is too hot. Moreover, if the drying process is not properly performed other materials, such as resins, tannins and other constituents of the wood can be lost. These constituents of the timber are important in imparting to it its natural characteristics and resistance to deterioration by natural agents such as wind and water.
In contrast with known drying processes, the present invention seeks to provide a process in which, in addition to the extraction of moisture from the wood, there is also a stabilization of the wood; this results in improved conservation of the form of the pieces of wood subjected to the drying process, of the original fibrous and porous structure of the wood itself, and finally of the content of resin, tannin and other substances which contribute to the natural resistance of the wood to natural agents of deterioration.
With prior art processes and known equipment it often happens in practice that the equipment is underutilised because there is only enough wood of one kind to partly fill the available space, this results from the fact that known processes for drying hard woods require different conditions from the known processes for drying soft woods. Even though only partly loaded the equipment still takes the same time to complete the process. This is evidently uneconomic and irrational. With this invention it has been found that it is possible to treat at the same time both a quantity of hardwood and a quantity of softwood so that the plant may be completely loaded up to its total capacity with wood of various kinds (hard, soft, resinous and so on) and to obtain the desired drying effect in a time substantially less than that which would be required with prior art methods by the kind of wood which takes the longest time to dry.